Subsea oil/gas fields may have a plurality of wells linked to a host facility that receives the oil/gas via flowlines. Such a field may have a subsea well architecture that employs either single or dual flowlines designed in a looped arrangement with in-line pipe line end termination (“PLET”) units positioned at selective locations for well access. The linkage between wells creates a need for PLETs to be deployed within prescribed target box areas to allow for well jumper connections to the flowline. These typically non-recoverable PLETS sit directly on unconsolidated soils on the seafloor and support connectors that allow fluid flow access between the wells and the flowline. Well jumpers connect the production trees on the wells to the flowline through the flowline connectors. For well testing or intervention operations, unless a well can be accessed through the tree, selected flowlines may be depressurized and a well isolated to flow fluids to or from a well. The PLET structure is also not typically recoverable by a mobile offshore drilling unit (“MODU”) once installed.
The subsea oil/gas field may also include processing systems or production manifolds between the wells and the u facility. Using a manifold system, each well has a well jumper attached to a manifold, consisting of either single or dual flowline headers accepting production from a single well jumper distributed into single or dual flowlines. The manifold provides flowline access valves to selectively isolate wells. In this manner, fluids may flow to or from an isolated well without having to depressurize both of the flowlines. Fluid flow and mechanical access for testing, intervention, or other operations may be done through direct connection with each well tree. Fluids may also flow to or from an isolated well from the host facility through one or both of the flowlines. If only one of the flowlines is depressurized, the dual well jumpers allow for fluid flow from the non-isolated wells to the non-depressurized flowline.
Independent of the well architecture, operational activities are typically performed on well throughout the life of the well. For example, well operations may include well/flowline circulation, intervention activities, bull heading/well kill, corrosion management, de-waxing, scale removal, or pigging. These and other well operations may be performed by connecting tools directly at the subsea wellhead/subsea tree location and/or at the host production facility. The direct access into the wellhead/subsea tree typically requires intervention vessels, special intervention tooling, shut-in of production and depressurization of at least selected flowline sections, multiple rig mooring, and additional anchor handling due to the satellite offsets between the wells.